Frames for windows or doors commonly comprise an outer peripheral frame which is entered into an opening in a wall. In some cases the frame includes a cross member which extends across from one side frame member to a second opposed side frame member and these cross members are known as mullions.
In some case the mullion is formed as a cross member separate from the peripheral frame which butts at its ends against the side frame members at their opposed positions.
In other cases the structure is formed by two separate frame portions each having four frame members arranged around an open interior where the frame members on one side are butted against one another to form the mullion.
It will be appreciated that such constructions can be used in the formation of windows and also commonly in the formation of patio doors which provide a similar mullion between a fixed glass pane on one side and a movable glass pane on the other side or between two sliding members.
In regard to window frame constructions, the arrangement can be used with fixed panes, sash frames and sliders and the different design arrangements to be used in these different constructions are well known to a person skilled in the art.